As described, the present invention relates to improved self-riveting elements or fasteners having a shaft or barrel portion and an integral head portion which may be permanently affixed to a sheet metal part or panel by riveting. Elements of this type are previously known, wherein the shaft is generally threaded and introduced in a pre-formed hole in the sheet metal part. The head portion then bears on one side of the metal part. The sheet metal part or panel is then shaped in a setting operation, such that the panel molds physically into a small groove in the shaft of the element, directly adjacent to the bearing surface on the underside of the head portion, thereby securing the element in a sheet metal part or panel. The underside of the head, adjacent the shaft, may include radial ribs and the panel is deformed over the ribs during installation, preventing relative rotation of the elements on the sheet metal panel. Such assemblies are frequently used in industrial production by the automotive and appliance industries to fasten another component to the assembly, which may consist of a second sheet metal part and fastener, such as a nut. The contact surface of the head portion is thus located on one side of the first panel, opposite the second fastening element, such that the sheet metal part is stressed by compression between the fasteners.
In practice, however, the previously known self-riveting elements of this type were not securely attached to the metal part, such that the element commonly loosened in shipping or storage before assembly, particularly where the sheet metal part is relatively thin as now used by the automotive and appliance industries. It is not uncommon for the riveting element to become lost or assume an orientation in the panel which is unacceptable for further processing of the sheet metal part, as described above. The loosening of the prior self-riveting elements of this type also sometimes resulted in inefficiency of the intended anti-rotation means, such that the element will rotate as the nut is assembled on the shaft portion, before the nut is tightened on the bolt. These difficulties are a particular problem in automotive body construction and other applications where the head portion of the riveting elements are located in an enclosed cavity following installation, which is no longer accessible for repair. If the fastening element freely rotates in the panel or is lost under these conditions, the object being manufactured, such as an automobile, can no longer be finished in regular production, but must be repaired at substantial expense. Obviously, these problems should be avoided, if possible.
Another problem, particularly with attaching a riveting fastener to thin sheet metal panels results from the fact that the anti-rotation ribs must have a certain height; that is, the height of the ribs from the contact surface on the underside of the head portion must be sufficient to prevent rotation. Where the sheet metal part is relatively thin, the ribs dent the panel to a degree such that the full strength of the sheet metal part is no longer available, which may lead to further problems.
Another disadvantage of self-riveting male fastener elements of this type is that the small groove in the shaft portion which receives the panel material to prevent pull-out is difficult to make and thus unnecessarily increases the cost of the fastener. Further, this radial groove results in an undesirable reduction in the strength of the bolt or screw fastener, including its fatigue properties, resulting from the sharp edges and reduction of the cross-sectional area of the shaft portion of the element. Further, because of the groove dimensions, the element may also be insufficiently secured to the sheet metal part, aggravating the tendency of the element to loosen in the sheet metal part or drop out, as described above.
Thus, a primary object of the present invention is to provide a self-riveting element of this type which can be manufactured and fixed to the sheet metal panel at a relatively low cost and wherein the risk of loosening or loss of the element out of the sheet metal part is reduced and preferably precluded. Another object is to provide a joint between the self-riveting element and panel which is as strong as possible and a self-riveting element or fastener which is suitable for attachment to thin sheet metal parts, including nonferrous sheet metal parts, such as aluminum or its alloys.